Method of insulating armature coils

ABSTRACT

Straight side portions of an armature coil adapted to be received in armature slots are insulated with insulating tapes containing a relatively hard and nonpliable epoxide resinous composition, while looped end portions are insulated with insulating tapes containing a relatively pliable long chain epoxide resinous composition to avoid damage to the insulation structure due to mechanical stress created during insertion of the coil into armature slots. Not only the interlayer insulation but also the ground insulation is formed by the above described two types of insulation tapes.

United States Patent I2 I I Inventors Appl. No. Filed Patented AssigneePriority Yoshiaki Kimura; H

Yoshlharu Sano; Ryoji Kumazawa; Ilisayasu Mitsui, all of Yokohama, Japan1 1,984

Feb. 17, 1970 Dec. 21, 1971 5 Tokyo Shibaura Denki Kabushlki KalshaHorikawa-cho, Kawasaki-shl, Kanagawaken, Japan Feb. 25, 1969 JapanMETHOD OF INSULATING ARMATURE COILS 6 Claims, 2 Drawing Figs.

U.S. Cl 156/56, 156/185,156/305,156/330,156/334, 310/208, 174/120 SRInt. Cl 1101b 3/40, HOlb 17/66 Field of Search 156/56,

Primary Examiner-Carl D. Quarforth Assistant Examiner-E. A. MillerAttorneysRobert E. Burns and Emmanuel J. Lobato ABSTRACT: Straight sideportions of an armature coil adapted to be received in armature slotsare insulated with insulating tapes containing a relatively hard andnonpliable epoxide resinous composition, while looped end portions areinsulated with insulating tapes containing a relatively pliable longchain epoxide resinous composition to avoid damage to the insulationstructure due to mechanical stress created during insertion of the coilinto armature slots. Not only the interlayer insulation but also theground insulation is formed by the above described two types ofinsulation tapes.

PATENIEU 05021 an FIG.

FIG.2

TEMPERATURE c) AwmmmwmQPQzC. m0 M4024 ill METHOD OF INSULATING ARMATURECOILS BACKGROUND OF THE INVENTION This invention relates to a method ofinsulating armature coils for electric machines and apparatus, moreparticularly formed armature coils for use in generators and motors ofvarious capacities which can be disposed in slots of the core withoutdamaging the coil insulation and have excellent tan 8- voltagecharacteristic and high insulating strength.

Armature coils for dynamoelectric machines of medium or highercapacities are formed in an oblong hexagonal or diamond configuration.Insulating tapes for insulating such coils are generally prepared byimpregnating a varnish solution into mica flakes or mica paper(sometimes designated as mica mat) lined or backed with paper, cotton orglass cloth, glass fiber, nonwoven cloth or the like. Varnish solutionsare prepared by dissolving a suitable insulating resin such as epoxide,polyester and silicone compound in an organic solvent such as toluene,xylene, methylethylketone, methylisobutylketone, ether, cellusolve andthe like. The tape is then wound about the coil. The coil sides, orstraight portions of the coil which are to be received in armature slotsshould be precisely finished to have a generally rectangular crosssection and flat sides. According to one method, side plates of metal orparchment paper are applied on four sides of the coil sides, and thentapes of heat shrinkable polyethylene or polyethylene-terephthalate arewrapped around the assembly. Then the heat is applied to cause the tapesto shrink to compress the insulation structure formed by the insulatingtape to eliminate air voids between insulation layers. By the heat andpressure applied in this manner, the resin is caused to set to form asolid and integral insulation structure. According to another method,coils wrapped with insulation tapes of the above described type arevacuum impregnated with a low viscosity solventless-type resin and arethen subjected to heat and pressure to form a void-free insulationstructure. As coils insulated by this vacuum impregnation method havefewer voids, they are particularly suitable for use in high-voltagedynamoelectric machines without the risk of generating corona discharge.

As is well known in the art, armature windings are wound as lapwindings, wave windings or chain windings, but generally the former twotypes are utilized. In the case of [zip winding, the configuration ofthe coil is usually oblong hexagonal and two sides of different coilsare received in each slot to form two-layered windings. When insertinghexagonal coils to form two-layered windings one side of the coil mustbe raised or held out of the slot whereby the coil ends are subjected tosubstantial mechanical stress, thus damaging the insulation. Especiallyin the case of high-voltage machines, the thickness of the groundinsulation increases with the voltage. Moreover, the interlayerinsulation should also be strengthened to withstand high surge ortransient voltage. As the thickness of the insulation structureincreases, damage thereof caused by lifting one side of the coil isincreased. When inserting coils utilizing a thermosetting resin as thebinder and the impregnating agent, the coils are heated to a temperatureranging from 70 to 90 C. to soften the resin thus alleviating damage tothe insulation. However, in high-voltage coils this solution is notsufficient.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide a novel method of insulating an armature coil of adynamoelectric machine having straight side portions adapted to bereceived in armature slots of the machine and looped end portionsextending beyond the armature slots.

A more specific object of this invention is to insulate the looped endportions with pliable insulation structures so as to minimizedegradation thereof due to mechanical stress applied to the coil when itis placed in the armature slots.

A further object of this invention is to provide an armature coil for adynamoelectric machine with its straight side portions insulated withrigid insulation structures which can be accurately formed to thedesired configuration and with its looped end portions insulated withpliable insulation structures.

According to this invention straight side portions of the armature coilare insulated with insulating tapes containing an epoxide resinouscomposition having a relatively high softening point or relatively lowpliability, whereas looped end portions of the coil are insulated withinsulating tapes containing another epoxide resinous composition havinga relatively low softening point or relatively high pliability.

As the first epoxide resinous composition of low pliability, any one ofmany well-known epoxide resins available on the market can be used.However, as the second epoxide resinous composition of high pliability,we use a long-chain epoxide resin prepared by reacting epichlorohydrinwith a member selected from the group consisting of a mixture of a majorproportion of dimer acid and a minor proportion of trimer acid;polyazelaic polyanhydride for example, Emily-3455-IBIAPA (sold rr-polybutadiene dicarboxylic acid by Emily Co.); and

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 is a perspective view of a portion of an armature coil embodyingthis invention and FIG. 2 shows characteristic curves to show thepliability of the resin utilized in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As diagrammatically shown inFIG. 1, an oblong hexagonal armature coil 1 for use in dynamoelectricmachines includes a pair of parallel straight side portions 2 which areto be received in armature slots and looped end portions 3interconnecting the opposite ends of straight side portions 2. Accordingto this invention, the looped end portions are insulated with insulatingtapes impregnated with an epoxide resin binder which softens at arelatively low temperature, whereas straight side portions 2 areinsulated with insulating tapes impregnated with an expoxide resinbinder which softens at a relatively high temperature. Thereafter, theinsulated coil is vacuum impregnated with a suitable impregnatingcompound and the coil is then heated under pressure to set the resin andcompound.

Generally, an epoxide resin is extremely hard and brittle after setting.To impart pliability to the insulation structure impregnated withepoxide resin, it has been proposed to incorporate a thermoplastic resinto epoxide or to employ aminoethylpiperazine, polyamide, etc., as thecuring agent. However, when the epoxide resin is made pliable in thismanner, its electrical characteristics are degraded.

According to this invention this problem is solved by using a long-chainpliable epoxide resinous composition mentioned above.

The details of the method of insulating armature coils is as follows:

Two types of mica tapes are prepared for forming coil insulations. Oneis used for insulating straight side portions and is prepared byapplying onto a thin insulation substrate a resinous compositionconsisting of an epoxide resin such as Epicoat 828 or Epicoat 1001 (soldby Shell Chemical Limited, U.S.A.), a hardening agent such ashexahydrophthalic anhydride (HHPA) or malenized linseed oil and a curingcatalyst such as benzyldimethylamine (BDMA). The coated substrate isthen heated to semicured state. The insulating tape thus obtained hasexcellent electrical and mechanical characteristics. The otherinsulating tape is used for insulating looped end portions and comprisesa mica paper or mat lined with a sheet of paper or nonwoven cloth whichcan be elongated to some extent and a semicured resinous compositionconsisting of Epicoat 1001, a flexible long-chain epoxide resin such asEpicoat 871 (sold by Shell Chemical Limited, U.S.A.), a hardening agentsuch as HHPA or dodecyl succinate anhydride (DDSA) and a curing catalystsuch as BDMA. The last mentioned resinous composition begins to softenat a temperature of from 30 to 50c., whereas the former begins to softenat a temperature of 80 C., as will be described with reference to FIG.2.

The mica tape of the second type is then wrapped around the loopedportions 3 of the coil, and that of the first type around the remainingportions of alternate turns or entire turns of the coil (includingstraight side portions 2) to form a so-called interlayer insulation.Each tape is wrapped for a required number of convolutions with half-lapjoints. In the second step the ground insulation is formed on theinterlayer insulation by wrapping the second mica tape about loopedportions while wrapping the first mica tape about the remaining portionsof the coil, each for a required number of convolutions with half-lapjoints depending upon the voltage to the ground. To decrease electricalvulnerability and to make easy the wrapping operation of the jointsbetween looped portions and other portions of the coil, tape laminationsare stepped. In the third step, the insulated armature coil is placed inan impregnating tank and is then subjected to an preliminary dryingprocess under vacuum. Then in the third step the coil insulation isimpregnated under vacuum with a solventless epoxide resin composition oflow viscosity (2 to 7 poise) and long pot life, and the resinouscompositions are caused to cure by heating at a temperature of 120 to160 C. for 15 to 30 hours, under pressure. The resinous composition ofthe impregnating varnish utilized in the third step consists of DX-200(sold by Shell Chemical Limited), a monoepoxide compound, e.g., benzylglycydylether and a hardening agent such as malenized linseed oil andHHPA. in carrying out this invention, in order to impart sufficientpliability to the looped end turns of the coil, it is important toincrease the quantity of the binder for bonding the mica tape to a valueseveral times that of the binder for the tape used to insulate otherportions. This prevents impregnation of the looped portions with theimpregnating resinous composition which is of less pliability and usedduring the the third step, thus preserving the high pliability of themica tape. As the backing material for the mica tape, ordinary glasscloth is not suitable for the tape utilized to insulate the loopedportions because glass tape has small elongation so that it cannotrelieve the stress concentrating at the looped portions when one side ofthe coil is raised. However, where especially high mechanical strengthis required, bias cut glass tape may be used. Generally, paper andnonwoven cloth are preferred.

The insulation structure obtained in this manner is a voidfree solidintegral structure, and the insulation strength thereof is not degradedby the mechanical handling of the coil required for placing it in thearmature slots. Moreover, the novel insulation structure has excellenttan 8-voltage characteristic and large breakdown strength. Thus, thisinvention is especially suitable for insulating armature coils for usein highvoltage, large-capacity dynamoelectric machines.

The following specific examples are given by way of illustration and arenot to be construed as limiting in any way the scope of the invention.All parts are by weight.

Example 1 Eighty-seven parts of Epicoat l00l, 67 parts of Epicoat 871which is a long-chain epoxide composition, 55 parts of HHPA and 0.2 partof BDMA were dissolved in a solvent consisting of 146 parts of tolueneand 63 parts of MIBK to prepare a varnish. The varnish was then causedto impregnate a thin mica tape lined with a thin nonwoven cloth toprepare a tape A for insulating looped portions or end turns of thearmature coil, said tape A containing 15 percent, by weight, of resinouscomposition in the case of mica flakes and 50 percent, by weight, in thecase of a mica mat. Then 15 parts of Epicoat 828, 30 parts of Epicoatl00l, 15 parts of malenized linseed oil, 10 parts of HHPA and 0.2 partof BDMA were dissolved in 70 parts of MIBK to obtain a varnish. Thisvarnish was used to impregnate a thin mica insulating tape to prepare atape B for insulating remaining portions of the coil, said tape Bcontaining 12 percent, by weight, of resinous composition in the case ofmica flakes and 20 percent, by weight, in the case 0T a mica mat.

In the first step, the tape A was wrapped about the looped portions ofthe coil and the tape B about the remaining portions of the coil to forma continuous interlayer insulation.

In the second step, the tape A was wrapped with several turns about theportion of the interlayer insulation around the looped portion, and tapeB was wrapped with several turns about remaining portions of theinterlayer insulation to form a ground insulation. According to theusual practice, a plurality of rectangular strands with thin turninsulations are stacked in two rows, and the stack is wrapped with tapeA or B to form interlayer insulation. At least two such stacks withinterlayer insulations are superposed on each other, and tape A or B iswrapped around the superposed assembly to form the ground insulation. Itis advantageous to form the ground insulation by alternate layers oftapes of mica flakes and tapes of mica mat.

in order to avoid electrical vulnerability, joints between insulationsaround the looped portions and remaining portions were stepped.

in the third step, a solventless epoxide resinous composition forimpregnation was prepared by admixing parts of HHPA as a hardeningagent, 40 parts of malenized linseed oil, 40 parts ofbutylglycidylether, and 120 parts of DX-200 (sold by Shell ChemicalLimited). The impregnating composition has a viscosity of 150centipoise. The armature coil prepared by the first and second steps wasvacuum impregnated with this impregnating composition in an impregnationtank, and the impregnated coil was then cured under pressure by heatingit to a temperature of 150 C. for 25 hours.

Example 2 in this example, tape A of example I is prepared bysubstituting 95 parts of DDSA for HHPA to function as the hardeningagent. This modified composition is more pliable as shown by curve a ofFIG. 2 than that of example 1 (curve b).

This modified tape was used to insulate looped portions of the coil. inthis case, however, only a mica mat tape was used to form the groundinsulation. In the third step, a solventless resinous compositionconsisting of 20 parts of Epicoat 828, 25 parts of butylglycidyletherand 57 parts of HHPA was used to vacuum impregnate the coil, and theimpregnated coil was cured by heating it to a temperature of 150 C. for25 hours.

The pliabilities of various resinous compositions are indicated in FIG.2, in which the ordinate represents the angle of twist in degrees andthe abscissa the temperature in degrees Centigrade. Curve a representsthe pliability of the resinous composition of example 2 for use inpreparing a mica tape for insulating the looper portions, and curve bthat of the resinous composition of example 1 for use in preparing amica tape for insulating the looped portions. Curve represents thepliability of the resinous composition for a tape utilized to insulatethe other portions of the coil, and d that of the solventlessimpregnating resinous composition.

Example 3 Process of example 1 was repeated except that a pliable micatape was prepared by using a resinous composition consisting of 335parts of Epicoat 1001, 80 parts of HHPA and 20 parts of a long-chainpolyazelaic polyanhydride sold under a trade name PAPA and employed toincrease pliability.

Example 4' PAPA utilized in example 3 was substituted by an equivalentacid value quantity'of a,m-polybutadiene dicarboxylic acid sold under atrade name of NlSSO-PB (3) by Nippon Soda Co., Limited, Japan, and theresulted resinous composition was used to prepare a pliable mica tapewhich was used in the same manner as in example 1.

For comparison coils with their looped portions insulated with aninsulating tape containing a pliable epoxide resinous composition,.forexample, Epicoat 781 prepared by reacting a mixture of acids consistingof a major proportion of long-chain dimer acid and a minor proportion oftrimer acid with epichlorohydrin or a modified epoxide resinouscomposition, wherein said acid components were substituted by alongchain acid such as polyazelaic polyanhydride or a5 w-polybutadienedicarboxylic acid and conventional coils with their all portionsinsulated with the same resinous composition were prepared and thesecoils were subjected to coil raise tests.

In the prior art armature coils the breakdown strength per 2 mm. of theinsulation structure was decreased to 60 to 75 kv. after coil raise from90 to 95 before coil raise, whereas that of the coils insulatedaccording to this invention was about 90 kv. before and after coilraise. This was caused by the concentration of the stress at the loopedportions when the coil was raised or bent up thus forming small cracksin the insulation structure. On the other hand, according to thisinvention since the looped portions are insulated by a pliableinsulation structure, as the upper coil is bent upwardly, the insulationstructure of the loop portions can bend just like the upper coilconductor to absorb the stress. Although slight changes occurs in theinsulation structure on the looped portions such a slight change doesnot result in any appreciable change in the electrical characteristics.

Heretobefore, the quantity of the resinous composition for bonding micawas made higher at the looped portions than at the remaining portions.For example, the quantity of the resinous composition at the loopedportions was 50 percent, by weight, for mica mat, or l5 percent for micaflakes whereas that of the resinous composition at the remainingportions was 20 percent for mica mat or l2 percent for mica flakes. lncoils with its entire portions insulated with mica tapes containing 20percent of the resinous composition for mica mat or 12 percent for micaflakes, the pliability of their insulation structure was lost by theimpregnating resin and its breakdown strength was decreased to 70 to 80kv. In contrast, in this invention use of much more quantity of theresinous composition at the looped portions than other portions resultsin higher pliability without loss of insulating strength.

Further, the result of test showed that the electrical characteristicsof the insulation structure for the looped portions are substantiallythe same whether it is formed by a mica tape containing mica mat or byalternate tapes of mica mat and mica flakes. This is important when oneconsiders that flake mica tape can be impregnated with at most 20percent of the resinous composition whereas mica mat tapes with up to 60percent of the resinous composition. Moreover, mica mat tapes are moreexcellent and of more uniform quality than mica flake tape, are easierto apply and have higher insulating strength.

Coils insulated in accordance with this invention are applicable tomachines having more than four coils.

We claim:

1. A method of insulating an armature coil including straight sideportions adapted to be received in armature slots of a dynamoelectricmachine and looped end portions extending beyond said annature slots,said method comprising the steps of applying a first insulating tapecontaining a first epoxide resinous composition having a relatively highsoftening point around at least said straight side portions of the coil,applying a second insulating tape containing a second longchain epoxideresinous composition more pliable than said first epoxide resinouscomposition around said looped end portions, impregnating an insulationstructure formed by said first and second insulating tapes with asolventless epoxide resinous composition, and heat curing said epoxideresinous compositions.

2. A method of insulating an armature coil including straight sideportions adapted to be received in armature slots of a dynamoelectricmachine and looped end portions extending beyond said armature slots,said method comprising the steps of applying a first insulating tapecontaining a first epoxide resinous composition having relatively highsoftening point around at least said straight side portions of the coilto form a first interlayer insulation, applying a second insulating tapecontaining a more flexible epoxide resinous composition than said firstepoxide resinous composition around said looped end portions to form asecond interlayer insulation contiguous to said first interlayer, thejoints between said first and second interlayer insulations beingstepped, applying said first insulating tape around said firstinterlayer insulation and applying said second insulating tape aroundsaid second interlayer insulation whereby to form a continuous groundinsulation, impregnating said ground insulation with a solventlessepoxide resinous composition, and heat curing said epoxide resinouscompositions.

3. The method according to claim 1 wherein the softening point of saidfirst epoxide resinous composition is about 30 to 50 C. whereas that ofsaid second epoxide resinous composition is about C.

4. The method according to claim 1 wherein comprises a long-chainepoxide composition prepared by reacting epichlorohydrin with an acidcomposition consisting of dimer and trimer acids.

5. The method according to claim 4 wherein the quantity of said trimeracid is smaller than that of said dimer acid.

6. The method according to claim 1 wherein said second epoxide resinouscomposition comprises a longchain epoxide composition prepared byreacting epichlorohydrin with an acid component selected from the groupconsisting of polyazelaic polyanhydride and a, w-polybutadienedicarboxylic acid.

2. A method of insulating an armature coil including straight sideportions adapted to be received in armature slots of a dynamoelectricmachine and looped end portions extending beyond said armature slots,said method comprising the steps of applying a first insulating tapecontaining a first epoxide resinous composition having relatively highsoftening point around at least said straight side portions of the coilto form a first interlayer insulation, applying a second insulating tapecontaining a more flexible epoxide resinous composition than said firstepoxide resinous composition around said looped end portions to form asecond interlayer insulation contiguous to said first interlayer, thejoints between said first and second interlayer insulations beingstepped, applying said first insulating tape around said firstinterlayer insulation and applying said second insulating tape aroundsaid second interlayer insulation whereby to form a continuous groundinsulation, impregnating said ground insulation with a solventlessepoxide resinous composition, and heat cuRing said epoxide resinouscompositions.
 3. The method according to claim 1 wherein the softeningpoint of said first epoxide resinous composition is about 30* to 50* C.whereas that of said second epoxide resinous composition is about 80* C.4. The method according to claim 1 wherein comprises a long-chainepoxide composition prepared by reacting epichlorohydrin with an acidcomposition consisting of dimer and trimer acids.
 5. The methodaccording to claim 4 wherein the quantity of said trimer acid is smallerthan that of said dimer acid.
 6. The method according to claim 1 whereinsaid second epoxide resinous composition comprises a long-chain epoxidecomposition prepared by reacting epichlorohydrin with an acid componentselected from the group consisting of polyazelaic polyanhydride andAlpha , omega -polybutadiene dicarboxylic acid.